PROJECT SUMMARY/ABSTRACT The goal of this project is to characterize the multifaceted inhibitory and tumor-targeting properties of SP2043, a type IV collagen-derived peptide, in triple negative breast cancer (TNBC) models. TNBC is a particularly lethal cancer owing to a high propensity for metastasis and limited treatment options. Attempts to limit the metastatic progression of TNBC using anti-angiogenic agents have not been very successful, in part due to lymphatic dissemination. However, attempts to block lymphangiogenesis using broad-range inhibitors was met with significant toxicity. Peptide inhibitors offer a unique opportunity to design potent inhibitors with low toxicity. SP2043 and its early analogs were found inhibit the activation of multiple growth factor receptors, including many related to both angiogenesis and lymphangiogensis (ie. VEGFR2 and VEGFR3). As a possible explanation for this multimodal inhibition, these peptides were found to interact with several species of integrins. Integrins are highly expressed in tumors and their vasculature and associated with the progression of metastatic disease. In addition to their roles in adhesion and migration, integrins can contribute to metastasis through the regulation of growth factor receptors by clustering them into large, functional protein complexes or by altering their intra-cellular trafficking. Disruption of these processes can have profound effects on receptor stability and signaling profiles, emphasizing the potential benefit for development of SP2043 as a therapeutic agent. Here, we propose to investigate the inhibitory mechanisms of SP2043 through their interactions with integrins as well as offset one of their major disadvantages, their short half-life in vivo, through their incorporation into tumor target-nanoparticles. Specific Aim 1 will use biophysical and cellular based methods to determine the affinity of SP2043 for specific integrin pairs and investigate the effects of this peptide on the stability of integrin-growth factor receptor signaling complexes. Specific Aim 2 will investigate the mechanism through which SP2043 influences cellular responses to growth factor signaling, including changes in the distribution of specific growth factor receptors and processes involved in vessel stability and permeability . Finally, in Specific Aim 3, optimal formulations for the anti-angiogenic activity of SP2043-coated nanoparticles will be investigated using mouse xenograft models of the MDA-MB-231 TNBC cell line in order to improve the bioavailability and test the efficacy of these compounds. Together, these experiments will allow for the better characterization of SP2043?s multimodal inhibition and pave the way for its development as a targeted therapy for the treatment of TNBC.